1. Field of the Invention
The instant invention relates to a novel process for preparing aminopropyltrialkoxysilanes and/or aminoalkylalkoxysilanes. More specifically, the invention relates to the platinum catalyzed addition of allylamine or N-substituted allylamines with trialkoxysilanes or alkylalkoxysilanes under pressure at 110.degree. to 210.degree. C. in the presence of a reaction promoter.
2. The Prior Art
The platinum catalyzed addition of allyl amine or N-substituted allylamines to trialkoxysilanes (I) offers a direct route to aminopropyltrialkoxysilanes. This reaction is well ##STR1## known and has been studied by many investigators. However, in order to obtain a reasonable conversion and yield, the process requires long reaction time and/or high platinum catalyst concentrations. For instance, U.S. Pat. No. 3,665,017 teaches the preparation of .gamma.-aminopropyltriethoxysilane and .gamma.-aminopropylalkylalkoxysilanes by refluxing allyl amine with hydrogenalkoxysilanes or hydrogenalkylalkoxysilanes in the presence of a platinum catalyst until the temperature of the reaction mixture reaches a constant level above 110.degree. C. The time required to reach the final temperature varied from 10 to 60 hours, depending upon the platinum catalyst concentration used and the presence or absence of a solvent having a higher boiling point than the components that were to be added to one another. Therefore, when a mixture of allyl amine and triethoxysilane containing 5% of ethyl silicate was heated in the presence of approximately 200 ppm platinum (as H.sub.2 PtCl.sub.6), the temperature of the reaction rose to 190.degree. C. in 14 hours to give a 71-79% yield of the desired product. But the time required increased to more than two days (56 hours) when the platinum catalyst concentration was decreased to about 66 ppm. Similarly, in U.S. Pat. No. 3,864,373 mixtures of .gamma.- and .beta.-amino-propyltriethoxysilane were prepared by heating allyl amine with trialkoxysilane in the presence of a platinum catalyst such as mesityl oxide platinum dichloride until the sump temperature reached approximately 135.degree. C. or for 24 hours (Zh., Obshch Khim, 42, (4), 858-862 (1972)). In the latter case, the temperature of the reaction mixture rose from 74.degree. C. to 125.degree. C. during the 24 hour heating period and the yield of aminopropyltriethoxysilane was in the range of 60 to 67%. Two Czech Patents obtained 57-71% of .gamma.-aminopropyltriethoxysilane by heating the reactants from 70.degree.-150.degree. C. in the presence of (CH.sub.2 .dbd.CHCH.sub.2 NH.sub.3).sup.+ PtCl.sub.3.sup.- (Czech C S No. 165,746) or of (Ph.sub.3 P).sub.4 Pt or (Ph.sub.3 P).sub.2 PtX.sub.2 (193.448).
Recently, a continuous process for the preparation of aminoalkoxysilanes was disclosed (Ger. (East) No. DDR151944). Thus the addition of organohydrosilanes to allyl amine in the presence of a solution or suspension of an addition catalyst in multi-stage, heatable reaction apparatus was carried out under ambient pressure in the temperature range of 110.degree.-135.degree. C. and with a contact time of from 3600-2400 seconds. According to the process, the reaction time was shortened considerably. However, the process requires several reactors and high platinum concentration (&gt;200 ppm).
Aminopropyltriethoxysilanes have also been prepared by heating the reactants in the presence of a platinum catalyst and a promotor (or co-catalyst) such as unsaturated ether (USSR No 372,228), ketone, carboxylic acids, keto-acids and esters (USSR No. 415,268) allyl alcohol (USSR No. 505647), epichlorohydrin (USSR No. 724,459) and dicarbon-nidoundecaborate K(C.sub.2 B.sub.9 H.sub.12-n R.sub.n.sup.- K.sup.+) (USSR No. 724,515). These reactions generally were carried out at atmospheric pressure and the platinum catalyst and promoter were heated together with allyl amine and the corresponding trialkoxysilane until the temperature of the reaction mixture reached 120.degree. C. or higher. For example, aminopropyltrialkoxysilanes were prepared by treating trialkoxysilanes with allyl amine in the presence of H.sub.2 PtCl.sub.6 (100 ppm) and 0.1-1.5% epichlorohydrin for 9-11 hours until the temperature of the mixture reached 120.degree. C. and then held at that temperature for another 2-3 hours. Yield of the aminosilanes was in the range of 58-70%. V. Vybrial and his coworkers have also studied the effect of various promoters which included: triphenylphosphine, triphenylarsine, carboxylic acids and their esters and some carbonyl compounds. The best modifier found was triphenylphosphine. When used in conjunction with H.sub.2 PtCl.sub.6 (.about.350 ppm Pt), it shortened the reaction time from 9.7 hours (H.sub.2 PtCl.sub.6 alone) to 6.5-7.3 hours. All these results indicate that even with 100-200 ppm of Pt, extensive reaction time is required in order to obtain reasonable conversions and yields.